Vitamin D supplements are beneficial for bone health, but a new study that analyzed data on more than 39,000 adults finds that Americans may be overdoing it. The number of U.S. adults taking daily vitamin D supplements between 1999 and 2014 increased by more than 17 percent, with three percent of the population exceeding the recommended upper dosage limit. Too much vitamin D poses a risk of adverse effects, including abnormally high levels of calcium in the blood and soft tissue, leading to vascular calcification. The recommended dietary allowance for vitamin D is 600 IU/d for adults 70 years or younger and 800 IU/d for those older than 70 years.